The major goals of this proposal are to use mouse model systems to explore the mechanisms by which three DNA alkylation repair pathways affect the etiology of cancer and in addition how they affect the sensitivity or resistance of animal tissues to chemotherapeutic alkylating agents. These three pathways are the Aaginitiated base excision repair pathway for the repair of 3MeA, epsilonA, epsilonG, hypoxanthine plus other base lesions, Mgmt-mediated DNA methyltransferase repair of O6/MeG DNA base lesions, and AIkB-homolog (Abh) mediated oxidative demethylation of 1MeA and 3MeC DNA base lesions. For these studies we will use two isogenic mouse null mutants, Aag -/- and Mgmt -/-, generated and characterized in the last funding period, and two new null mutants, Abhl,2, -/-, to be generated in the next funding period. The interaction of these alkylation repair pathways with the following will be explored: metal overloading diseases, chronic infection and chronic inflammatory diseases; other damage response pathways regulated by p53 and Atm. The specific aims are summarized here. Aim 1: Generation and characterization of mice lacking Abhl and Abh2 function. Aim 2: Inflammation, DNA alkylation damage and repair, and pathological responses. Aim 3: Biological interaction of alkylation repair pathways with each other and with the DNA damage response 3athways regulated by Atm and p53. In each case we will determine how the manipulation of these pathways influences the sensitivity of tissues, organs and whole animals to spontaneous and alkylation induced cell _illing, apoptosis, whole animal lethality, and tumorigenesis. In addition we will further explore how the Mgmt pathway interacts with the DNA mismatch repair pathway at the both the mismatch recognition step and at the excision steps. These studies will contribute to our understanding of our natural defenses against the toxic and carcinogenic effects of endogenous and environmental alkylating agents as well as alkylating agents used for cancer chemotherapy.